Pipelines used to transport products such as fuel, gas or hazardous liquids, particularly fuel pipelines, require periodic maintenance which involves cleaning their outer surfaces and providing them with protective coating, e.g., coating for protecting the outer surfaces of the pipes from corrosion. Since these pipelines reach thousands of kilometers in length, the maintenance is effected in stages, viz. successively on sections thereof, which have a length in the order of tens of meters. Each section is subjected to maintenance at intervals of a few years, but in view of the great length of the pipelines, the overall maintenance operations are extremely heavy and costly.
Currently, each pipeline section is exposed by digging at the sides and under the pipeline, to distance the outer surfaces of the pipes from the surrounding ground sufficiently to permit to carry out on said outer surfaces the required maintenance operations. In many cases, the pipeline is laid in or crosses hard ground, such as rock formations, which is very difficult to dig out, and requires lengthy and expensive operations. It will be appreciated that while the ground may have been comminuted to some extent on the sides, when a trench was dug for the laying of the pipeline, the bottom of the trench is intact and can be formed by a hard rock mass. In addition, digging underneath the pipeline in any ground type will compromise the integrity of the trench bed and additional costs are incurred in restoring the trench bed to a state suitable for supporting the pipeline. So far, no method or apparatus is known in the art that will overcome these difficulties and render the maintenance of the pipelines easier and more economical. More specifically, no method or apparatus is known that will permit to avoid having to dig below the pipeline, often into hard rock beds.
It will be appreciated that any damage to a pipeline, involving failure thereof and spillage of the transported liquid, would constitute, apart from the economical damages, a major economical disaster, and therefore those responsible will never carry into practice a maintenance method that involves even a very small probability of such damage and failure.
U.S. Pat. No. 4,218,044 describes a pipeline lifting device which comprises a detachable sling consisting of an upper part and a lower part. The upper part carries a self-propelled trolley. The lower part of the sling is articulated by rings with mutually articulated, supporting shoes. The shoes are moved by hydraulic cylinders. Both parts of the sling are interconnected with each other by projections and slots. In order to operate the device, a pit is dug of a sufficient size for accommodating the said lower part of the sling. Said lower part is placed on the pipeline and then turned around it for putting it on the bottom of the ditch. The self-propelled trolley is moved along the pipeline until the said upper part of the sling is engaged with the lower part. Then the hydraulic cylinders can be actuated to lift the pipeline. Since the bottom of the pipeline has a vertical spacing from the bottom of the ditch before the pipeline is lifted, the ditch cannot be so long that said vertical spacing be such as to damage the integrity of the pipeline. When the pipeline is lifted, the amount of the lifting is added to the said vertical spacing. As a result, the length of the ditch, along which maintenance can be carried out, is limited, this device only permits maintenance of a short length of the pipeline at a time. Additionally, its operation requires an initial digging underneath the pipeline, with the drawbacks hereinbefore set forth. Therefore this device is of limited, if any, value.
It is therefore a purpose of this invention to provide a method that will permit to avoid digging under the pipeline into the trench bed, particularly when it is hard rock bed.
It is another purpose of the invention to provide such a method that avoids with absolute certainty any damages to the pipeline, that might result in failure thereof.
It is a further purpose of this invention to provide such a method which involves considerable savings in terms of time and costs in the maintenance of pipelines.
It is a still further purpose of this invention to provide an apparatus for carrying out the aforesaid method.
It is a still further purpose of this invention to provide such an apparatus which is error-proof, so that it eliminates any danger of damage or failure of the pipeline as a consequence of the maintenance operations.
It is a still further purpose of this invention to provide such an apparatus that can be easily transported from section to section of the pipeline.
It is a still further purpose of the invention to provide such an apparatus that can be easily operated by workers who have no particular skill.
Other purposes and advantages of the invention will appear as the description proceeds.